Fluidized catalytic cracking (FCC) is one of the major refining methods used in the oil refining industry. The FCC process is employed to crack materials consisting essentially of petroleum-type hydrocarbons to produce products such as fuels for internal combustion engines and heating oils. The cracking process is usually performed in a vertically oriented conduit, or riser including a reactor vessel, that forms part of an FCC system. During the process, hot catalyst particles in an aerated (fluidized) state are typically introduced into a bottom portion of the riser and induced to flow upward. A hydrocarbon feedstock is mixed with steam to become partially fluidized and injected into the catalyst flow as the catalyst travels through the riser, which creates cracking reactions that breakdown the hydrocarbon feedstock into a simpler (lighter) molecular form.
Optimal cracking conditions in an FCC process require a substantially immediate and homogenous mixing of the catalyst and the hydrocarbon feedstock. Such mixing is difficult to achieve, however, and stratified regions of hot catalyst and cold hydrocarbon feedstock typically appear within the catalyst-hydrocarbon flow. Over-cracking and thermal cracking of the hydrocarbon molecules typically occur in the catalyst-rich areas of the flow. Conversely, incomplete cracking of the hydrocarbon molecules usually occurs in hydrocarbon-rich flow regions. These factors can substantially reduce the overall yield of the FCC process. In addition, over-cracking, thermal cracking, and incomplete cracking have undesirable side-effects such as deactivation of the catalyst within the riser due to coke laydown, regeneration of the catalyst within the regenerator due to the combustion of air and residual coke, and the production of excessive amounts of lower-boiling-range gaseous reaction products, e. g., propane and butane gases.
Hence, effective methods for mixing the catalyst and the hydrocarbon feedstock within the reactor vessel are critical to the cracking process. To ensure proper mixing, spray nozzles have been devised that introduce the hydrocarbon-steam mixture into the upward flowing catalyst; however, the nozzles currently available for use in FCC units have significant limitations. First, the nozzles can generate an uneven spray pattern that reduces liquid contact between the hydrocarbon-steam mixture and the catalyst, which in turn impedes homogeneous mixing leading to over-cracking, thermal cracking and/or incomplete cracking of the hydrocarbon molecules. Second, the nozzle covers protrude from the inner vessel wall into the catalyst stream, which leads to premature erosion of the nozzle components and a reduced life cycle of the nozzle; additionally, as the nozzle cover erodes, the geometry of the nozzle's internal flow passages can change resulting in altered spray patterns, which can in turn reduce the consistency and overall output of the yield of the FCC process. Further, the protruding nozzle covers reduce the flow area of the catalyst and create down stream low pressure zones in the vessel that generate eddy currents that facilitate erosion of the nozzle cover. Still further, due to the constant temperature fluctuations within the FCC vessel, the nozzle covers are susceptible to thermal shock, which causes cracking which further contributes to their reduced life cycle. Similar limitations are present in other refining processes that utilize nozzles to introduce fluids into a mixing vessel, such as reduced crude conversion (RCC) processes.
In some spray nozzle applications, ceramic nozzle covers have been used in place of standard metallic alloy covers. Though ceramic covers can offer many advantages, joining a metal to a ceramic is a challenge because ceramics have extremely high melting points and are chemically relatively inert preventing them from being directly welded or glued; therefore, mechanical joints of various types are employed. However, the mechanical joints currently available often fail prematurely and without warning due to fluctuating thermal expansion and thermal contractions caused by temperature variances in the applications of the nozzle.
Therefore, to improve the yield of FCC and other refining processes and reduce maintenance expenses associated with frequent nozzle cover and joint replacements, there is a need for a spray nozzle that generates a consistently flat spray pattern for improved homogeneous mixing, reduces down stream low pressure zones and eddy currents to minimize catalyst erosion, and/or employs a nozzle cover that has a reduced profile to minimize protrusion into the catalyst stream to, in turn, reduce cover erosion and maximize the flow area of the catalyst, is made up of an erosion resistant material, and is ductile enough to avoid thermal shock. Further, there is a need for a joint/coupling device that is capable of maintaining a tight seal between the nozzle cover (outlet) and the fluid inlet and can withstand thermal shock caused by constant temperature fluctuations.